[sdiy] ASM VCO tips wanted.....

[Oren Leavitt]

Hi Steve,

Referring to the ASM-1's new home at Magnus' site:

http://rubidium.dyndns.org/~magnus/synths/friends/stopp/asm1vco-1.1.pdf

Is the CV summer working correctly?
Check the voltage at the base of Q1 relative to ground.
With trimmer P1 in the mid-position and nothing connected to CV inputs, the voltage there should be around zero volts.
You should see this voltage decrease by approx 18mV as you increase the the control voltage by 1 volt and vice versa as you decrease the CV.

If that checks ok, then check the oscillator core by disconnecting the collector of Q2 from Q3,C2,U3.
Connect this (- input of U3,C2,Q3) to V+ through a 100K resistor - it should oscillate.

HTH,
Oren

-----Original Message-----
From: RevTor at aol.com
Sent: Apr 2, 2004 12:31 AM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] ASM VCO  tips wanted.....

Hello all, I have my ASM here, and one of the oscillators wont oscillate.  I've gone over the thing numerous times and have replaced the 3140, 311, and the FET (its now a 2n3819 this should be OK right?)
here's the schemo:
www.home.swipnet.se/cfmd/synths/friends/stopp/asm1vco-1.1.pdf
(thanks Gene Stopp!!)

anyway, all the panel controls and jacks check out OK, and all the resistors and caps are the exact same as the other osc (which works)  The voltages at the chips are all OK, and the trimpots are okay too.  
The SAW out isnt stuck at +v, but instead I noticed that the voltage at SAW out slowly decreases, and the rate of decrease increases when I reduce the value of the cap on the FET.. : ) follow that?  heheh
so it basically acts like a very low freq osc.  the panel controls have no impact on this rate either... 

so, if anyone has any ideas about this I'd be greatly appreciative!!  I'd like to get it fully operational and now that Ive spent many hours mulling over the circuit, i'm officially on a mission!!!!!!!!!!!!!!!!!!!

thanks all,
see ya at AHNE!!!!!

~Steve M
revtor at aol.com